- Hitchhikking: almost free, but no guarantee of safety
- Carpooling internet site: cheap but the guy can cancel for no reason and if you are in a hurry, it could be annoying
- Trains and buses: They are really cheap in Eastern Europe (Poland, Hungary and else)
- Trains in Western Europe are really awesome with the Eurorail Pass. Just check on the internet the prices. Because in Switzerland without that pass you would kill your wallet in two days ;) about 2 years ago
A number of years ago I used a Eurail pass and I thought it was fantastic.
I had an unlimited 2 months all countries pass, which was quite pricey, but well worth every cent! In some countries it also covered local transit, and in some cases provided discounts.
If you aren't bothered about what actual places you visit, I met a guy who would just grab the cheapest fares. if there was a special to go to Spain for 10 euro, he'd jump on it. He managed to get around a lot of Europe at a good price.
I'm pretty sure there are bus options (like a eurail pass) as well for a reasonable price, but it depends on how you feel about busses - I get motion sick so wouldn't consider it an option. about 2 years ago